Spontaneous Thermal Convection in the Vicinity of Electrolyte/Water Interfaces

We present theoretical evidence for transient roll-cell convection induced in the vicinity of freshly prepared electrolyte/water interfaces. The mechanism relies on a hitherto unrecognized type of double-diffusive convection. Electrolyte diffusion down the strong concentration gradient at the interface produces local heating just below the interface as the electrolyte becomes more dilute. If the concentration gradient at the interface is sufficiently large, temperature gradients on the order of one Kelvin per centimeter can be induced by this mechanism. We assume the horizontal electrolyte/water interface is contained in a long prism with a square vertical cross section and that the electrolyte solution is denser than the supernatant water layer. Provided that the sidewalls of the prism are thermally conducting, convection commences at the junction of the interface (at half the height of the square section) and these walls. In each vertical semi-cross-section, two roll cells evolve at the interface and the lower cell rapidly gains intensity at the expense of the counter-rotating upper cell. After a short period of time the lower cell migrates diagonally downward to lie just beneath the interface and the associated region of local heating. Although the fluid velocities associated with this roll cell initially increase with time, they do not appear to be sufficiently strong to distort the vertical stratification of the electrolyte's concentration profile. In a cylindrical annulus standing on its circular base the dominant roll cell takes the form of a toroidal vortex resembling a Taylor vortex. Copyright 1999 Academic Press.